
REPRODUCTION IN ANIMALS
71
parts such as hands, legs, head, eyes,
ears etc. The stage of the embryo in
which all the body parts can be
identified is called a foetus (Fig. 6.9).
When the development of the foetus is
complete, the mother gives birth to
the baby.
place inside the egg shell during this
period? After the chick is completely
developed it bursts open the egg shell.
In animals which undergo external
fertilisation, development of the embryo
takes place outside the female body. The
embryos continue to grow within their
egg coverings. After the embryos develop,
the eggs hatch. Y
ou must have seen
numerous tadpoles swimming in ponds
and streams.
Viviparous and Oviparous Animals
We have learnt that some animals give
birth to young ones while some animals
lay eggs which later develop into young
ones. The animals which give birth to
young ones are called viviparous
animals. Those animals which lay eggs
are called oviparous animals. The
following activity will help you
understand better and differentiate
between viviparous and oviparous
animals.
Activity 6.2
Try to observe eggs of the following
organisms – frog, lizard, butterfly
or moth, hen and crow or any other
bir
d. Were you able to observe eggs
of all of them? Make drawings of the
eggs that you have observed.
The eggs of a few animals are easy
to observe because their mothers lay
them outside their bodies. These are
examples of oviparous animals. But you
would not be able to collect the eggs of
a dog, cow or cat. This is because they
do not lay eggs. The mother gives birth
to the young ones. These are examples
of viviparous animals.
Internal fertilisation takes place in
hens also. But, do hens give birth to
babies like human beings and cows? You
know that they do not. Then, how are
chicks born? Let us find out.
Soon after fertilisation, the zygote
divides repeatedly and travels down the
oviduct. As it travels down, many
protective layers are formed around it.
The hard shell that you see in a hen’s
egg is one such protective layer.
After the hard shell is formed around
the developing embryo, the hen finally
lays the egg. The embryo takes about 3
weeks to develop into a chick. You must
have seen the hen sitting on the eggs to
provide sufficient warmth. Did you know
that development of the chick takes
Fig. 6.9 : Foetus in the uterus
Uterus